Method of preparing zing mercaptides and method of preparing a greases containing zinc mercaptides



United States Patent i Allen F. Millikan and Ernest T. Fronczak, CrystalLake, 111., assignorsto The Pure Oil Company, Chicago, 111.,

a corporation of Illinois No Drawing. Filed Nov. '5, 1957, Ser. No.694,520 11 Claims. el. ,z1s2 42.7

This invention relates to a lubricating composition containing a majorportion of a mineral lubricating oil and a sufficient amount of. a metalmercaptide to form a gel therein and impart to said lubricating oil theproperties of a colloidal gel structure.

Numerous metal salts, polyvalent metal soaps, selenomercaptans, heavymetal alcoholates, alkaline earth metal phenates, aryl metal oxides,alkali metal naphthenates and .the like :aredisclosedas addends formineral lubricating oils. .In general, .these .addends are used in smallamounts ranging from 0.01 to 5.0 weight percent with the minerallubricating oils for such purposes as inhibiting oxidation or sludgeyas:detergents, foam inhibitors, extreme pressure agents to prevent pistonring sticking, as oiliness agents, for ,color stabilization, to combatcorrosion, and associated purposes. The present invention relates to theproblem of iorminga solid phase of certain metal mercaptides in acolloidal solution in the mineral lubricating oil which resultant gel isstable and has utility as a grease or gel-lubricant exhibitingextremepressure properties. The distinction :to :be drawn between the gelledlubricating ,oil composition of this invention and the prior artcompositions "lies in its gel properties, the method of its formation,the materials used and their preparation, and the amounts foundnecessary to attain the stable gel or liquid-in-solid solution. 7

Because of these interdependent :discoveries, theinvention alsodistinguishes over such art as states that metal compounds and the likecan be used to thicken lubricating oils. Atrue *geludiifers remarkably.firom athickened oil as will be demonstrated. Also, the inventiondistinguishes over the common gelling agents, such as the sodium,aluminum, lithium, barium, lead and magnesium soaps of fatty acids ornaphthenic acids, 'orinorganic thickeners such asfinely .divided silicaor bentonite, in that the gellingagen'tsrof this invention serve aldua'lfunc tion, rthatfof forming a true colloidal gel and imparting otheruseful properties to the mineral lubricating oil.

In accordance with :this invention, it has been discovered that the zincsalts of aliphatic, straight-chain mercaptans, in which the .alkyl grouphas *from 8 to 1-8 carbon atoms per molecule, incorporated in a minerallubricating oil in a particular manner, form a gel or grease structurehaving stability and .extreme pressure qualities. The zinc mercaptidesof this invention have the following general formula:

WhereinlRis a straight-chain, saturated alkyl group containing-f-rom 8.to -18 carbonatoms. Thus, inaccordance with the foregoingqdefinition, Rmaylaenneoctyl, n-nonyl, n-decyl, nedodecyl, -n4etradecyl, n-hexadecyl,or n-octadecyl.

Specific. examples include:

, Zinc l-dotlecylmercaptide Zinc '1--n-octyl mercaptide ,Zinc ln-nonylmercaptide Zinc l-n-decyl mercaptide 12,963,434 Patented Dec. 6,1960 Zinc l-n-tetradecyl mercaptide Zinc l-n-hexadecyl mercaptide Zincl-n-octadecyl mercaptide Accordingly, it becomes a primary objective ofthis invention to provide a new type of gelling agent for minerallubricating oils.

Another object of the invention is to provide a gelled minerallubricating oil containing a metal mercaptide of the general formula:

wherein R is a straight-chain, saturated alkyl radical having from 8 to18 carbon atoms.

Still another object of the invention is to provide a grease compositioncontaining a sulficient amount of the foregoing specified metalmercaptide to form a gel structure, which grease exhibits extremepressure characteristics, and is stable in storage and use.

These and further objects of the invention will become apparent as theinvention is described in greater detail.

The invention will be demonstrated by reference to a number of examplesto illustrate the technique of preparation, the physical properties ofthe completed compositions, comparative data showing metal mercaptideswhich do not work, and the relationship of the amounts necessary to forma gel.

THE METHOD OF PREPARATION 2NaOH+2C gH SeH+ 2C H SeNa-l-H O ZnSO +2C HSeNa (CHI-12586) 2ZH+N32S04 Also, the prior art shows that leadoctadecyl selenomercaptan can be prepared by reacting basiclead acetatein a glacial acetic acid-alcohol solution with octadecylselenomercaptan.Aluminum alcoholates are prepared by the direct reaction of aluminummetal with an alcohol in the presence of iodine, and zinc alcoholatesare prepared by direct reaction of zinc chloride with an alkali metalalcoholate. The reaction of. diisobutyl phenol with sulfurchloride-toyield diisob-utyl hydroxy phenyl sulfide, which is reacted with bariumhydroxide octahydrate to yield the barium salt, proceeds quite readilywhen the mixture is blown with nitrogen and heated to 215 F. However,metal salts of these kinds, though used in con centrations of 10% byweight or more in a mineral lubricating oil to thicken same, do not forma stable gel structure. Such compositions break down during use andstorage.

Attempts to react zinc oxide directly with a mercaptan by heatingstoichiometric mixtures were unsuccessful; apparently .no reaction takesplace. When calcium oxide was mixed with a mercaptan irra solution ofliquid ammonia, orrefluxed with a mixture of mercaptan, toluene, andwater, no reaction took place. "Similarly, an attempt --to react calciumchloride with a mercaptan inliquid ammonia was negative.

.It has been found, in accordance with this invention, that thehigher-molecular-weight mercaptans react with zinc oxide, with orwithout the presence of mineral lubricatingoil, if liquid ammonia isused. Further, it has Example 1.Preparatin of zinc I-dodecyl mercaptideand grease therefrom To make a reaction medium, 12.2 g. (0.15 mole, 0.30equiv.) of zinc oxide was aded to approximately 250 m1. of liquidammonia with stirring. Then a mixture of 40.5 g. (0.2 mole, 0.2 equiv.)of l-dodecyl mercaptan, 50 ml. toluene, and 50 ml. of 85 vis/ 100 V1.neutral was slowly added as stirring continued. As the ammoniaevaporated at room temperature, the mixture became somewhat gelatinous,and 300 ml. of toluene was added to the mixture. Heating and stirringover steam for an hour reduced the system to an essentially liquidphase. Excess zinc oxide was removed by vacuum filtration. Most of thetoluene was removed by nitrogen stripping over steam. The productanalyzed 8.0 wt. percent zinc and 7.2 wt. percent sulfur. Calculated onthe basis of zinc content as found by analysis, the product contained57.3% zinc l-dodecyl mercaptide, and on the basis of sulfur content asfound by analysis, 52.5% zinc l-dodecyl mercaptide. In the formulationimmediately below, this mercaptide solution was used as produced(average of 55% zinc mercaptide in 85 vis neutral oil) in an amount of20%.

A grease was prepared using the following ingredients:

Zinc l-dodecyl mercaptide *11.0 85 vis/ 100 V1. neutral 9.0 200 vis/90V.I. neutral 53.5 160 vis/90 V.I. bright stock 26.5

Wt. percent 100.0 From solution produced as described.

All components were blended together and heated to 110 C. with stirring.The hot liquid was poured into a shallow pan and cooled rapidly; in theprocess of cooling, a firm gel structure formed. The firm gel was thenreduced to a softer, buttery grease texture by shearing the gel in acolloid mill. The resulting grease was of the order of a No. 0 or No. 1N.L.G.I.-consistency-grade grease, with an A.S.T.M. grease droppingpoint of approximately 200 F.

Example 2.Preparation of zinc J-hexadecyl mercaptide Exacty 6.1 g.(0.075 mole, 0.15 equiv.) of zinc oxide was added to approximately 75ml. of liquid ammonia with stirring. To this reaction medium, a liquidmixture of 25.9 g. (0.1 mole, 0.1 equiv.) of l-hexadecyl mercaptan, 31ml. toluene, and 31 ml. or 85 vis neutral was added slowly. At roomtemperature, the ammonia was allowed to evaporate, with stirring. Thetoluene was then partially removed by heating and stirring over steam. Agelatinous product formed that was identical in appearance to that ofthe zinc l-dodecyl mercaptide product of Example #1.

Example 3.Preparati0n of zinc t-dodecyl mercaptide Exactly 6.1 g. (0.075mole, 0.15 equiv.) of zinc oxide was added to approximately 75 m1. ofliquid ammonia with stirring. To this, a liquid mixture of 20.3 g. (0.1mole, 0.1 equiv.) of t-dodecyl mercaptan, 24 ml. toluene, and 24 ml. of85 vis/ 1000 V1. neutral was added slowly. After the ammonia hadevaporated, toluene was stripped off by heating to 300 F. with stirring.Excess zinc oxide was removed by filtration of the hot product. Thefiltrate was clear yellow, and exhibited extreme pressure properties, asaforementioned, but the product was not gelatinous. Analysis: 8.3% zinc,corresponding to a 60.5% concentration of zinc t-dodecyl mercaptide inoil.

Exactly 12.2 g. of zinc oxide were added to 40.5 g. of l-dodecylmercaptan, and the mixture was heated at 200 C. for 2 hours. At the endof this time, practically all of the zinc oxide separated from themercaptan and there was no evidence of salt formation.

Example 6 Exactly 6.6 g. of calcium oxide were slurried in 200ml. ofliquid ammonia. Then 33.4 g. of l-octyl mercaptan and 150 ml; of toluenewere added with stirring. The mixture was heated as in Example No. 1.Again the metal oxide separated from the mixture after removal of theliquid ammonia, with no evidence of reaction.

Example 7 Example 6 was repeated using calcium chloride instead ofcalcium oxide with the same negative results.

Example 8 Exactly 12.2 g. of calcium oxide were mixed with 33.4 g. ofl-octyl mercaptan in 300 ml. of toluene and 10 ml. of water. The mixturewas heated to a reflux temperature of about C. for 20 hours. Again therewas no evidence of reaction or salt formation.

Example 9 Exactly 20.3 g. (0.25 mole; 0.5 equiv.) of zinc oxide wasadded to approximately 200 ml. of liquid ammonia. To this was addedslowly, with stirring, a solution of 59.1

g. (0.5 mole, 0.5 equiv.) of l-hexyl mercaptan in 150.

m1. of ether. The reaction mixture was stirred until the ammonia wassubstantially all evaporated. The product was filtered off and driedunder vacuum. There Was 72.0 g. of mercaptide product, a yield of 96%.Analysis of zinc l-hexyl mercaptide: theor: 21.8% zinc, 21.4% sulfur;found: 21.9% zinc, 21.4% sulfur. It was not possible to form a gel withlubricating oil using the zinc l-hexyl mercaptide thus prepared.

Example 10 In the manner of Example 9, zinc cyclohexyl mercaptide wasprepared in liquid ammonia using 8.2 g. (0.1 mole, 0.2 equiv.) of zincoxide and 23.8 g. (0.2 mole, 0.2 equiv.) of cyclohexyl mercaptan insolution in ml. of ether. The yield was 32.1 g. of product (against 29.6g. in theory) suggesting that the product was not completely dry.Analysis of product found: 21.2% zinc, 18.5% sulfur. Again, it was notpossible to form a gel with lubricating oil using the zinc cyclohexylmercaptide thus prepared.

Example 11 In the manner of Example 9, zinc l-octyl mercaptide wasprepared in liquid ammonia using 15.9 g. (0.195 mole, 0.39 equiv.) ofzinc oxide and 50.3 g. (0.34 mole, 0.34 equiv.) of n-octyl mercaptan insolution in 150 ml. of ether. There resulted 59.4 g. of mercaptideproduct, a yield of 96%. Analysis of zinc l-octyl mercaptide: theor:18.4% zinc, 18.0% sulfur; found: 21.2% zinc; 16.1% sulfur. The analysisis partially explained by the excess of zinc oxide in the charge whichwas not separable from'the final product. The mercaptide thus preparedformed a weak gel structure with lubricating oil, but it was notpossible to incorporate as much as 10% of the mercaptide in thccomposition.

Example J2 In this experiment an attempt was made toprepare leadl-dodecyl mercaptide, Pb(SC H by the liquid ammonia technique used inExamples 9, 10, 11 and 12 (wherein no oil diluent was used). By reactinglead oxide with dodecyl mercaptan, a product was separated and driedunder vacuum. Analysis of this product showed 52%lead and 6 .0% sulfur.Theoretically this product should contain 34% lead and 10.5% sulfur.This product exhibited no gelling tendencies.

vention between'about 1.0 to 15.0 wt. percent may be incorporated in.the oleaginous carrier. Other addends such as oxidation inhibitors,pour point depressions, VI improvers and the like may be incorporated incompositions of this invention. Greases prepared using at least anamount sufiicient to provide about 0.25 weight percent sulfur to as highas 2.0 wt. percent sulfur in the final composition are stable andqualify as greases.

Any mineral oil or lubricating oil may be used to formulate compositionsusing the zinc mercaptides of this invention. Mineral oils ofMid-Continent, West Coast, Texas or Pennsylvania origin may be used.Refined mineral oils of predominantly paraffinic'nature form a preferredclass of 'liquid carrier agent for the zinc mercaptides. Suchlubricating oil fractions as neutrals and bright stocks which have beensolvent refined, dewaxed and clay treated in a manner known to the artform a preferred class of carrier useful in preparing greases and othergel compositions for lubrication where anti-wear properties areparamount. The physical properties of the particular oils used in theexperiments described herein are given in the following table.

TABLE-PHYSICAL PROPERTIES OF MINERAL OILS API Viscosity Wt. Neut. OilGrav. Flash, Fire Color, Pour, OR VI Percent N 0.

7 degrees F. NPA F. S (1948) 85/100 N eutral- 35. 8 385 430 79. 3 56. 037. 6 1. 0 5 0.0 103 0.07 0. 03 200/90 Neutral 29. 3 430 485 207 10746.5 1V 0 0. 01 91 0. 4 0.09 160/90 Bright Stoe 23.9 575 650 3,291 1,165 171.8 6 5 1. 2 92 0. 80 0. 42

. Example 14 v In addition to their unique gelling properties in mineralUsing the technique of Example 13, an attempt was made to preparestannous l-dodecyl mercaptide,

There was some evidence of a gelling effect, although it was distinctlyminor as compared with the gel formation experienced with the zincmercaptides. Analysis of the product-showed in one sample 34.8% metaland in another 10.6% metal, and in the first sample 13.4% sulfur andinthesecond sample 15.6% sulfur. Theoretically, this productshould-contain 22.8% metal and 2.8% sulfur. I Example 15 In thisexperiment cadmium oxide and dodecyl mercaptan were reacted using thetechnique of Examples 9, 10, 11 and 12 to prepare cadmium l-dodecylmercaptide, Cd(SC H Analysis of the product revealed in one sample 39.8%metal and in another sample 0.0% metal, and 9.0% sulfur for bothsamples. Theoretically, this product should contain 21.8% metal and12.4% sulfur. There Was no evidence of gelling tendencies.

The foregoing experiments indicate that the straightchain zincmercaptides coming within the definition of this invention are unique intheir properties of forming a stable grease or gel. The co-existence ofzinc and sulfur in the molecule points to their utility as extremepressure agents. In general, between about 1.0 wt. percent to as high as99.0 wt. percent may be used with a mineral lubricating oil base. Undercertain conditions it is contemplated that the zinc mercaptides of thisinvention may be used as lubricants per se, without a mineral oil base.A composition containing an amount of the zinc mercaptides of thisinvention suflicient to incorporate about 0.25 weight percent of sulfurtherein has been found to exhibit incipient gel properties. A thickenednon-gel composition is formed when an amount of the zinc mercaptides ofthis invention is used to incorporate less than 0.25 Weight percent ofsulfur in the total composition, i.e.,- 0.20 weight percent sulfur. Forpurposes of preparing greases using the zinc mercaptides of this inoils,the straight-chain zinc mercaptides should be of value for other useswhere thickening, or bodying, and/ or extreme pressure properties aredesired. In these applications where gelling is not requisite, thetertiary and secondarymercaptides are also of value. Thus the zincmercaptides should be of value as additives to lubricating oils toincrease viscosity and impart extreme pressure qualities, and inlubricant formulations for operations suchas metal cutting and stamping,and wiredrawing. They should also be of interest for protective coatingsas agents to increase the viscosity of vehicles used in paints,varnishes and lacquers, to adjust consistency, to modify. brushing andspraying properties, to decrease the ra'teof sedimentation and preventthe formation of a hard cake, to improve flat-finish coatings, and tofacilitate the grinding of fine particles for paints and lacquers. Inthe plastics industry they should have merit for formulating plasticizercompositions, and as internal lubricants. In the manufacture of inks,they should have value as thickeners and dispersion promoters.

Regarding the method of preparation found to apply herein, the ammoniaappears to act as a solvent and/or catalyst for the reaction. Assuming,without limiting the invention thereto, that the ammonia catalyzes thereaction, it may function to form an ammoniacomplex intermediate whichis decomposed in the heating steps. In this regard other liquidnitrogenous bases may be used such as liquid primary and secondaryamines. In carrying out the method, the zinc oxide is mixed with atleast a molar equivalent of the corresponding mercaptan in a solution ofthe liquid nitrogeviscosity of the mixture and ease the handlingthereof. After mixing the reactants at room temperature for about 1hour, the ammonia, if used, is allowed to evaporate. If an amine isused, it can be removed by heating over a steam bath with nitrogenstripping or with a slight vacuum. Any excess zinc oxide is removed byfiltration, preferably aided by a vacuum. The toluene or other solventis removed by nitrogen stripping over stream.

Where the mercaptides of this invention are prepared in situ in amineral lubricating oil or other oleaginous liquid, the resultingproduct solution can be readily blended to yield the compositionsdesired. By adding about to 30% by weight of an oil solution containingfrom 40% to 60% by weight of the zinc mercaptide, good grease structuresmay be formed. Where the mercaptides are prepared without a mineral oilpresent, they may be dispersed in a mineral oil to form a stable gelstructure by violent mixing or homogenization. Although the methodherein is applicable to the preparation of mercaptides having R groupsof less than 8 carbon atoms, such mercaptides do not exhibit the gelforming propensities of the mercaptides having R groups of 8 to 18carbon atoms.

The invention is only limited by the appended claims.

What is claimed is:

1. The method of producing zinc mercaptides of the general formulawherein R is a straight-chain, saturated alkyl group containing from 8to 18 carbon atoms, which comprises mixing zinc oxide with at least astoichiometric amount of the corresponding mercaptan in a solution of aliquid nitrogenous base of the group consisting of liquid ammonia,ethylamine and propylamine at ambient temperatures for a time sufficientto complete the formation of the zinc mercaptide, removing thenitrogenous base from said mixture and recovering said zinc mercaptide.

2. The method in accordance with claim 1 in which between about 0.075 to0.15 mole of said zinc oxide is reacted with between about 0.1 to 0.2mole of said mercaptan and said liquid nitrogenous base is ammonia.

3. The method in accordance with claim 1 in which the liquid nitrogenousbase is liquid ammonia.

4. The method in accordance with claim 1 in which the liquid nitrogenousbase is ethyl amine.

5. The method in accordance with claim 1 in which the liquid nitrogenousbase is propyl amine.

6. The method of preparing a grease composition containing a minerallubricating oil and a suflicient amount of a zinc mercaptide of thegeneral formula.

wherein R is a straight-chain, saturated alkyl group containing from 8to 18 carbon atoms, to impart a grease gel structure thereto whichcomprises dissolving at least a stoichiometric amount of zinc oxide in aliquid nitrogenous base of the group consisting of liquid ammonia, ethylamine and propyl amine, adding thereto a mixture comprising thecorresponding mercaptan and a mineral lubricating oil, maintaining saidmixture at ambient temperatures until the formation of said zincmercaptide is complete, removing said nitrogenous base from saidreaction mixture, heating said mixture at about C. for a time sufficientto homogenize same to a homogeneous liquid, filtering any unrcacted zincoxide therefrom, and blending the resulting oil solution of the zincmercaptide with a mineral oil to form a grease consistency.

7. The method in accordance with claim 6 in which said blending isaccomplished by heating said oil solution and added mineral oil,followed by rapid cooling, and the resultant gel is reduced to a greasetexture by milling.

8. The method in accordance with claim 6 in which said product is zincl-dodecyl mercaptide prepared by the reaction of 0.15 mole of zinc oxidewith about 0.2 mole of l-dodecyl mercaptan in a liquid ammonia solution.

9. The method in accordance with claim 6 in which the liquid nitrogenousbase is liquid ammonia.

10. The method in accordance with claim 6 in which the liquidnitrogenous base is ethyl amine.

11. The method in accordance with claim 6 in which the liquidnitrogenous base is propyl amine.

References Cited in the file of this patent UNITED STATES PATENTS2,228,500 Bergstrom Jan. 14, 1941 2,229,528 Shoemaker Jan. 21., 19412,289,795 McNab July 14, 1942 2,350,544 Zimmer et al. June 6, 19442,413,531 Verbanc Dec. 31, 1946 2,480,823 Morris et al. Sept. 6., 19492,510,765 Stewart June 6, 1950

6. THE METHOD OF PREPARING A GREASE COMPOSITION CONTAINING A MINERALLUBRICATING OIL AND A SUFFICIENT AMOUNT OF A ZINC MERCAPTIDE OF THEGENERAL FORMULA.